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Finding ourselves between physics and biology

By Joselle, on June 19th, 2013

The Institute of Physics (IOP) Biological Physics Group has a conference coming up June 24 to June 26 in Brighton, UK. The title of the conference is what first got my attention: Physics of Emergent Behavior/From single cells to groups of individuals.

The following text appears on the conference home page to introduce their interest in emergent collective behavior:

Biological systems are often conceptualised as networks of interacting genes and proteins. Nevertheless, a simple analysis of the fundamental genetic programs is often not sufficient to explain higher-level functions such as multi-cellular aggregation, tissue organization, embryonic development, and collective behaviour of groups of individuals. Furthermore, various aspects of these processes are often emergent properties of the underlying complex system, irrespectively to its microscopic details. In the past few years, larger scale experiments allowed the construction of statistical mechanics models of biological systems directly from real data, producing immense progress in our understanding of emergent collective behaviour in biology.

On their list of invited speakers is Dante Chialvo from the National Research Council of Argentina. He happened to be first alphabetically and, since his work is described as exploring “the interface of physics and biology on a variety of problems,” I decided to try to find some of his papers and/or talks. Chialvo’s work is largely involved in finding evidence to support the idea that the brain itself is in, what physics calls, a critical state. The rationale for proposing this idea is presented at the beginning of a paper that Chialvo co-authored with Enzo Tagliazucchi in 2012.

Complexity, in simple terms, is all about how diversity and non-uniformity arises from the uniform interaction of similar units. In all cases, the dynamics of the emergent complex behavior of the whole cannot be directly anticipated from the knowledge of the laws of motion of the isolated parts. Early forerunners of complexity science, namely statistical mechanics and condensed matter physics, have identified a peculiar scenario at which, under certain general conditions, such complexity can emerge: near the critical point of a second order phase transition. At this point, complexity appears as a product of the competition between ordering and disordering collective tendencies, such that the final result is a state with a wide variety of dynamic patterns exhibiting a mixture of order and disorder.

…From the cognitive side, brain’s complexity is an almost obvious statement: the ultimate products of such complexity are, for instance, the nearly unpredictable human behavior and the underlying subjective experience of consciousness, with its bewildering repertoire of possible contents. However, the proposal that the same mechanisms underlying physical complexity also underlie the biological complexity of the brain is surprisingly recent…. Being a relatively recent proposal, the consequences of such hypothesis are still far from clear.

Characteristic of a critical state is the subtle balance between order and disorder whose manifestation is being observed in neuronal activity. An article discussing very recent work appeared on APS’s website. In a talk Chialvo gave in 2010, he argues that it is reasonable to expect this hypothesis to be true. He begins his argument with a simple question: “Why do we need a brain at all?” His answer is also simple. The brain is necessary to navigate a complex, critical world. By this he means that the world itself rests on the border between order (subcritical) and disorder (supercritical) where the critical state is understood as one in which islands of order are bordered by the edges of disorder.

In a sub-critical world everything would be simple and uniform – there would be nothing to learn. In a supercritical world, everything would be changing all the time – it would be impossible to learn.

The brain took shape to navigate in a complex, critical world. But why must the brain itself be critical? Simple again.

In a sub-critical brain memories would be frozen. In a supercritical brain, patterns change all the time so no long term memory would be possible. To be highly susceptible, the brain itself has to be in the (in-between) critical state.

It was on this thought that my attention became focused. It created the impression of the brain (or the organism) and the world (or the universe) as joined, or interlocked. Chialvo’s answer to ‘why a brain at all?’ seems right, since organisms and their worlds are fully interactive – they belong to each other. At life’s most fundamental levels, it makes sense that an effective brain would acquire a structure that somehow matches its world. But I think it’s interesting to extend this view of the brain (as it has to do essentially with learning) to our more purely intellectual pursuits as well. Considering this biological notion of criticality could shed a new light on how it is that we come to understand our experience in the symbolic forms created in the arts and the sciences. This brings my mind back again to the way David Deutsch once expressed the baffling awareness we seem to have of aspects of our origins, ones that lie far outside our time and space. I’ll finish with reproducing it once again.

The one physical system, the brain, contains an accurate working model of the other, the quasar, not just a superficial image of it (though it contains that as well) but an explanatory model embodying the same mathematical relationships and the same causal structure… The faithfulness with which the one structure resembles the other is increasing with time….…Physical objects that are as unlike each other as they could possibly be can, nevertheless, embody the same mathematical and causal structure and do it more and more so over time…This place is a hub which contains within itself the structural and causal essence of the whole of the rest of physical reality.